Cacti 0.8.6e and earlier does not perform proper input validation to protect against common attacks, which allows remote attackers to execute arbitrary commands or SQL by sending a legitimate value in a POST request or cookie, then specifying the attack string in the URL, which causes the get_request_var function to return the wrong value in the $_REQUEST variable, which is cleansed while the original malicious $_GET value remains unmodified, as demonstrated in (1) graph_image.php and (2) graph.php.